问题如下:
Suppose that put options on an asset with strike prices USD 30 and USD 35 and the same time to maturity cost USD 4 and USD 7 (respectively). How can these options be used to create (a) a bear spread and (b) a bull spread?
解释:
(a) A bear spread is created by buying the put option with a strike price of USD 35 and selling the put option with a strike price of USD 30. (b) A bull spread is created by buying the put option with a strike price of USD 30, selling the put option with a strike price of USD 35, and adding the present value of USD 5 to the portfolio.
最后半句话什么意思呀